At least some of the original 1895 Winchesters were drilled & tapped for a Lyman receiver sight made just for that rifle.  I have seen replicas of that sight cataloged, by Buffalo Arms, IIRC. 

If you search past discussions on this forum, I think you can find a discussion about a modern mount for long-eye-relief scopes suitable for use with Krag rifles.  Modifying that mount to fasten on a bar or block held to the dovetail for your rear sight ought to be much less than $400.

Finally, I shoot a Uberti "High Wall" single shot in 30-40, with a windage & elevation adjustable tang sight and a Lyman 17A front sight.  If the tangs on your rifle are long enough, and if you have room behind the bolt when the action is open, a tang sight may be helpful.